The present invention relates to a method and apparatus for stuffer box crimping a multifilament yarn, of the general type disclosed in WO 03/004743 A1.
For stuffer box crimping a preferably freshly spun, synthetic multifilament yarn, a feed nozzle pneumatically advances the yarn into a stuffer box chamber. To this end, the feed nozzle comprises a yarn channel, into which a conveying medium is introduced under a high pressure. Together with the conveying medium, the multifilament yarn advances from the yarn channel of the feed nozzle into a stuffer box chamber directly downstream thereof. Inside the stuffer box chamber, a yarn plug is formed, so that the action of the conveying medium causes the fine filaments of the yarn to collect in loops and coils on the surface of the yarn plug. Preferably in its upper region, the stuffer box chamber comprises a gas permeable wall, so that the conveying fluid is able to leave the stuffer box chamber for being removed by suction.
To obtain an as uniform plug formation as possible and thus a crimp of the yarn that is as even as possible, it is necessary that in particular the conveying forces acting upon the yarn plug, as they develop, for example, because of the impact pressure effect of the conveying medium leaving the yarn channel of the feed nozzle, and the frictional forces acting upon the yarn plug, be at a defined ratio to each other. Thus, it is known to raise the conveying pressure of the feed nozzle for increasing the conveying speed. However, in this connection one must make sure that the conveying pressure does not result in blowing the yarn plug out of the stuffer box chamber, because the frictional forces between the yarn plug and the stuffer box chamber wall are unable to produce adequate retaining forces.
Basically, there exist two possibilities of forming inside the stuffer box chamber an as uniform plug as possible. In a first variant, the formation and advance of the yarn plug inside the stuffer box chamber is largely determined by friction. In this case, the frictional forces acting between the yarn plug and the stuffer box chamber wall are decisive for building up retaining forces, so that a defined force ratio is active between the conveying pressure of the conveying fluid and the retaining forces, and that thus a uniform advance of the yarn plug prevails within the stuffer box chamber.
In a second variant, a pair of feed rolls is arranged directly at the outlet end of the stuffer box chamber. These paired feed rolls remove the yarn plug from the stuffer box chamber. Thus, the speed of the yarn plug and yarn plug formation is largely determined by the speed of the feed rolls.
In both cases, it is common to remove conveying fluid emerging from the stuffer box chamber by additional suction. To this end, it is common to connect a source of vacuum to an expansion chamber, which substantially surrounds the walls of the stuffer box chamber. By adjusting a defined suction effect, a further parameter exists to influence the plug formation within the stuffer box chamber. However, the use of this additional controlled variable gives rise to the problem that an intensive suction causes volatile components, such as, for example, residues of a yarn lubricant that adhere to the yarn, to be carried along and to cause contaminations. Furthermore, a precise and reproducible adjustability of the suction effect is needed to be able to perform fine adjustments for forming and advancing the plug.
It is therefore an object of the invention to further develop a method and an apparatus of the initially described type for stuffer box crimping a multifilament yarn such that the plug formation in the stuffer box chamber can be influenced by a suction stream of the conveying fluid in a precise and reproducible manner.
A further object of the invention is to provide a reliable and rapid removal of the suction stream from the stuffer box chamber.